1. Field of the Invention
The present invention relates to a display comprising a light-emitting device array and a drive scheme to operate such. More specifically, the present invention provides a method to operate the light emitting device array in response to a stream of input image data to provide dynamic control of light emitting device array to deliver a composite image on a front panel.
2. Description of the Prior Art
Conventional liquid crystal displays (LCD), or similar light modulating displays, typically operate with an array of liquid crystal light valves modulating the light from a static light source. Dynamically controlled light sources have been proposed to operate in conjunction with the light modulators to deliver enhanced image quality where the light source intensity is controlled in accordance with the image data. It is perceivable that a better image enhancement is achieved with a higher degree of partition of dynamically varied light sources. For example, a greater benefit of image enhancement can be obtained in a multiple partition of controlled light sources than a single controlled source illuminating the entire screen. Similarly, a greater power efficiency is achievable in systems that comprises higher degree of partitioned light sources.
Dynamic control of light source in the real time requires light sources responding fast enough to varying drive current as to synchronize with the refreshing image data. In this regard, a light source based on light emitting diode (LED) offers a greater advantage than a cold cathode fluorescent lamp (CCFL), as the response time of LEDs is orders of magnitude faster than CCFL.
Light emitting diodes have been used in display applications as lighting elements, either as direct light emitting image pixels or as light sources from which the light is modulated by light modulators such as LCD light valves. Examples of the first application includes organic light emitting diode display (OLED) and discrete LED billboard. An example of second application is LED backlight. In all such display systems, a common challenge is the uniformity and stability of LED components. More specifically, the issue involves the requirement of a narrow distribution of initial spectra of the LEDs, as well as the controllability of subsequent time dependent decay. These issues have received substantial attention, but the current solutions are costly, or involves substantial technically complexity. This is especially so for a system comprising a large number of LED elements. For example, one current solution for the initial spectra control is sorting (binning) the LED elements and select specific spectral distribution for a certain product application. A solution for the time dependent decay, which varies from one LED element to another, and between different colors, is to construct build-in light sensors to detect the light output of selected LED elements. It is conceivable that a sorting procedure causes yield to drop and cost to increase. It is also conceivable that implementing sensor, while practical for a small number of LED elements, increases system complexity and cost substantially for a large LED system.
The present invention addresses these issues by providing a system solution which includes a structural aspect, a drive scheme aspect, and a system design aspect.
Examples of liquid crystal display (LCD) as light modulators and backlight construction are provided in U.S. Pat. No. 3,881,809, U.S. Pat. No. 4,540,243, U.S. Pat. No. 4,772,099, and U.S. Pat. No. 6,489,952, all of which are hereby incorporated by reference.